Conventional boiler furnaces for making electricity have water walls composed of tubes to contain water and members to connect the tubes. The furnace has a rectangular shape composed of four water walls. The water walls are composed of boiler tubes and connecting members. Each corner has a fuel/air nozzle which injects the mixture of fuel and air into the furnace. For a pulverized coal boiler, the nozzle injects fuel and air at a tangential direction to the assumed position of the fire in the furnace. Some boilers employ a super-heating zone above the furnace to absorb the heat and prevent it from going up the chimney. But the intense fire makes thermal NOx due to a temperature that can exceed 1,000° C. The higher the firing temperature, the more thermal NOx is produced.